1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to a gassing insulator assembly for the line conductor assembly of electrical switching apparatus, such as circuit breakers. The invention also relates to line conductor assemblies for electrical switching apparatus.
2. Background Information
Electrical switching apparatus, such as circuit breakers, for example, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions.
Circuit breakers, for example, typically include a set of stationary electrical contacts and a set of movable electrical contacts. The stationary and movable electrical contacts are in physical and electrical contact with one another when it is desired that the circuit breaker energize a power circuit. When it is desired to interrupt the power circuit, the movable contacts and stationary contacts are separated. Upon initial separation of the movable contacts away from the stationary contacts, an electrical arc is formed in the space between the contacts. The arc is undesirable for a number of reasons. Among them is the fact that the arc results in the undesirable flow of electrical current through the circuit breaker to the load. Additionally, the arc, which extends between the contacts, often results in vaporization or sublimation of the contact material itself. Therefore, it is desirable to remove and extinguish any such arcs from the contacts as soon as possible upon their propagation.
To facilitate arc extinguishing, circuit breakers typically include arc chute assemblies adjacent to the opening path of the separable contacts. The arc chute is constructed of a number of spaced plates extending transverse to the arc. As the movable contact is moved away from the stationary contact, the movable contact moves past the ends of the arc plates, with the arc being magnetically drawn toward and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken-up and extinguished by the arc plates. Examples of arc chutes are disclosed in U.S. Pat. Nos. 7,034,242; 6,703,576; and 6,297,465.
To facilitate arc removal from the separable contacts, an elongate arc runner is typically mounted with one end in close proximity to the stationary contact and an opposite end in close proximity to the arc chute assembly in order to provide a surface for the arc to run away from the contacts and toward the arc chute. This protects the contacts from damage due to arcing. The arc is formed on the stationary contact and must travel across a joint to the arc runner. At relatively low currents, the electromagnetic force on the arc may not be adequate to force the arc to cross this joint. One end of the arc may remain on the stationary contact, severely eroding that contact.
Also, when the arc is created on the stationary contact, it is more likely to travel along a sharp edge or corner of the part. Arc runners often have a slot up the center of the part to provide an attractive edge for the arc to run along. The edge of the slot encourages the arc to travel up the center of the arc runner, engaging the arc chute near the center thereof and extinguishing the arc relatively sooner. However, use of such slots can weaken the arc runner and lead to failure. Additionally, at lower current levels, the arc may be attracted to the laterally extending edge of the stationary contact instead of the slot in the arc runner. This may prevent the arc from running up the arc runner or cause the arc to run to one side of the pole where it may track along the inside wall of the arc chamber.
There is a need therefore for electrical switching apparatus with an improved arrangement for extinguishing arcs generated during current interruption.
There is a more specific need for such an improved arrangement for directing the arc from the stationary contact into the arc chute.
There is also a need for an improved arrangement for keeping an arc away from the edges of the arc runner while passing from the stationary contact to the arc chute.